1. Field of the Invention
The present invention relates to micro-machined structures and, more particularly, to a method and an apparatus for selectively actuating movement of micro-machined structures using electrostatic forces.
2. Description of the Related Art
Typically, silicon micro-machine structures are actuated by electrostatic attractive forces between resiliently mounted elements maintained at different voltage potentials. The attractive force between the elements is proportional to the square of the voltage difference. Nevertheless, insulators disposed between or near the elements tend to accumulate charges. These accumulated or residual charges may result from gas ions accumulated on the surfaces of the elements or the redistribution of charges in the insulators as a result of the electric field. Consequently, the elements drift apart over time even though the applied voltage potentials remain the same, thereby decreasing the accuracy of the actuation mechanism. Such accumulation of charges can reduce or even cancel the applied electric field.
One solution is to recalibrate the actuation mechanism from time to time. But calibration procedures tend to be time-consuming and highly disruptive to a user's normal operations as the systems must be taken off line periodically.
Accordingly, there is a need for an electrostatic actuating mechanism and method for controlling the movement of micro-machines and which does not cause the micro-machines to accumulate charges.